With applications ranging from diagnostic procedures to radiation therapy, the importance of high-performance medical imaging is immeasurable. As such, new advanced medical imaging technologies continue to be developed. Digital medical imaging techniques represent the future of medical imaging. Digital imaging systems produce far more accurate and detailed images of an object than conventional film-based imaging systems, and also allow further enhancements of the image to be made once an object is scanned.
Tomography is a two-dimensional radiographic imaging technique in which a cross-sectional image of a selected plane in an object is obtained, while details in other planes are blurred. Tomosynthesis is an advanced three-dimensional radiographic imaging technique in which several 2-D images of an object are taken at different angles and/or planes, and then these images are reconstructed as a 3-D image of the volume of the object that was imaged. Unlike conventional x-ray imaging techniques, tomosynthesis provides depth information about an area of interest within an object being imaged, such as a tumor or other anatomy within a patient. Tomosynthesis also enables any number of 2-D tomographic image slices to be reconstructed from a single scanning sequence of x-ray exposures, without requiring additional x-ray imaging, thereby making tomosynthesis a desirable characterization tool.
Generally, in digital tomography systems, an x-ray source is positioned on one side of an object being imaged, while an x-ray detector (i.e., an amorphous silicon flat panel x-ray detector) is positioned on an opposite side thereof. Generally, in amorphous silicon flat panel x-ray detectors, an amorphous silicon array is disposed on a glass substrate, and a scintillator is disposed over, and is optically coupled to, the amorphous silicon array. The x-ray source generally sweeps along a line, arc, circle, ellipse, hypocycloid, or any other suitable geometry, emitting a beam of x-rays towards the scintillator. The scintillator absorbs the x-ray photons and converts them to visible light. The amorphous silicon array then detects the visible light and converts it into electrical charge. The electrical charge at each pixel on the amorphous silicon array is read out and digitized by low-noise electronics, and is then sent to an image processor. Thereafter, a 2-D cross-sectional image is displayed on a display, and may also be stored in memory for later retrieval. A series of 2-D cross-sectional images may be reconstructed using 3-D reconstruction algorithms, to incorporate depth information into a final 3-D image, if desired.
Accurate alignment of the x-ray source with respect to the x-ray detector is critical to good image resolution in radiographic imaging systems. Phantoms are often used for calibrating and/or validating the alignment of film-based x-ray systems, where it is difficult to quantify x-ray levels or signal levels accurately. However, one drawback with film-based x-ray systems is that, generally, they only allow a visual assessment of the image sharpness to be made. Digital radiographic imaging systems, such as digital linear tomography systems, and any other radiographic imaging systems that allow the image to be digitized for numerical analysis, lend themselves to allowing accurate quantitative measurements of the alignment and/or image resolution or sharpness to be obtained. However, there are presently no known quantitative analysis systems and methods that use discrete spatial and frequency methods to precisely align such imaging systems so that optimal images can be obtained therefrom.
Therefore, it would be desirable to have systems and methods that utilize discrete spatial and frequency analysis to accurately quantify the mechanical alignment of radiographic imaging systems, thereby allowing for the precise mechanical alignment thereof so that optimal image resolution can be obtained therefrom. Additionally, it would be desirable to have simple-geometric-shaped phantoms that were useful for such purposes.